Heckler & Koch USPEdit
Design work on a new family of pistols commenced in September 1989 focused primarily on the U.S. commercial and law enforcement markets. In 1991, USP prototypes participated in rigorous testing alongside H&K's entry in the OHWS (Offensive Handgun Weapon System) program requested by the U.S. Special Operations Command (USSOCOM) and which would later result in the Mk 23 Mod 0. The USP prototypes were then refined in 1992, based on input from the OHWS trials and the design was finalized in December of the same year. The USP was formally introduced in January 1993 with the USP40 model (the base version) chambered for the increasingly popular .40 S&W cartridge, followed soon by the USP9 (using the 9x19mm Parabellum cartridge), and in May 1995—the USP45 (caliber .45 ACP).
The USP marked the first time H&K chose to incorporate many traditional handgun design elements, such as those of John Browning's M1911, in one pistol. Two principles guided its development—the first being the use of a molded polymer frame, and the second being the creation of a "pistol paradigm". Heckler & Koch observed the strong points of its previous successful pistols for insight in developing the USP. Previous H&K pistol innovations include the unique squeeze-cocking mechanism of the P7, the precise roller-delayed blowback operation of the P9S, and the plastic frame and double action only trigger system used in the VP70Z. In contrast to these ambitious designs, the USP uses a Browning-style cam-locked action, similar to that developed by John Browning for use in the Hi-Power pistol.
The USP is a semi-automatic pistol with a mechanically locked breech using the short recoil method of operation. This rather conventional lock-up system has a large rectangular lug over the barrel’s chamber that rides into and engages the ejection port cut-out in the slide. When a cartridge is fired, pressures generated by the ignited powder drive the cartridge casing back against the breech face on the slide, driving back both the barrel and slide as they remain locked together in the manner described above. After 3 mm (0.12 in) of unrestricted rearward travel, the projectile has left the barrel and gas pressures have dropped to a safe level. A shaped lug on the underside of the barrel chamber comes into contact with a hooked locking block at the end of the steel recoil spring guide rod, lowering the rear end of the barrel and stopping the barrel's rearward movement. The recoil spring assembly is held in place by the slide stop lever’s axis pin and a round cut-out at the front of the slide. For enhanced reliability in high-dust environments, the locking surface on the front top of the barrel’s locking lug is tapered with a forward slope. This tapered surface produces a camming action which assists in positive lock-up in the presence of heavy fouling and debris.
One of the most significant features of the USP is the mechanical recoil reduction system. This system is incorporated into the recoil spring assembly, located below the barrel and consists of a heavy, captive coil spring around the guide rod. Designed primarily to buffer the slide and barrel and reduce recoil effects on the pistol components, the system also lowers the recoil forces felt by the shooter up to 30%. The USP recoil reduction system is insensitive to ammunition types and does not require adjustment or maintenance. It functions effectively in all USP models. Using this same recoil reduction system, one of the related H&K Mk 23 .45 ACP pistols fired more than 30,000 high pressure +P cartridges and 6,000 proof loads without damage or excessive wear to any major components. Abuse and function-testing of USPs have seen more than 20,000 rounds of .40 S&W fired without a component failure. Milspec environmental tests were conducted in high and low temperatures, in mud, immersed in water and in salt spray. In one particular test, a bullet was deliberately lodged in the barrel and another bullet was fired to clear the obstruction. The barrel was successfully cleared with only minor structural deformation and continued to produce consistent groups when test fired for accuracy.
Major metal components on both the USP and Special Operations Pistol are corrosion-resistant. Outside metal surfaces, such as the steel slide are protected by a proprietary "Hostile Environment" nitride finish. Internal metal parts, such as springs, are coated with a Dow Corning anti-corrosion chemical to reduce friction and wear.
The USP is composed of a total of 54 parts and is broken down into 7 major components for maintenance and cleaning: the barrel, slide, recoil spring, recoil spring guide rod, the frame, slide stop and magazine. This is done by retracting the slide back to align the slide stop axis pin with the disassembly notch on the left side of the slide and withdrawing the axis pin.